Golf balls having layers made from functionalized ethylene copolymers

ABSTRACT

Golf balls having a core and containing at least one surrounding layer made from a functionalized ethylene copolymer having a linear or substantially linear structure are provided. The core may be made of a polybutadiene rubber material. The functionalized ethylene copolymer composition may be used to form any layer in the golf ball structure such as, for example, an outer core, intermediate layer, inner cover, and/or outer cover. The composition may be blended with ionomeric or non-ionomeric resins such as polyamides, polyurethanes, polyureas, polycarbonates, polyesters, and polyacrylates to form the layer. The resulting layers provide the golf ball with improved resiliency and impact durability.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to golf balls containing at least one layer made from a composition comprising a functionalized ethylene copolymer. More particularly, the layer contains a functionalized ethylene copolymer having a linear or substantially linear structure. The composition may be used to form any layer in the golf ball structure such as, for example, an outer core, intermediate layer, inner cover, and/or outer cover. The resulting layers provide the golf ball with improved physical properties including resiliency and impact durability.

2. Brief Review of the Related Art

Polyethylene copolymers modified by incorporating polar functional groups into the polymer are generally known. These compositions include ionomer resins, which generally refer to ionic copolymers of an olefin such as ethylene and a vinyl comonomer having an acid group such as methacrylic, acrylic acid, or maleic acid. The copolymers contain inter-chain ionic bonding as well as covalent bonding. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the copolymer. Commercially available ionomer resins are used in different industries and include numerous resins sold under the trademarks, Surlyn® (available from DuPont) and Escor® and Iotek® (available from ExxonMobil). Ionomer resins are available in various grades and identified based on the type of base resin, molecular weight, type of metal ion, amount of acid, degree of neutralization, additives, and other properties. Manufacturers of golf balls often use ionomer resins to construct ball covers. In general, golf ball covers made with such ionomer resins have a hard surface and show good durability and cut/shear-resistance.

Golf balls having layers made from non-ionomer olefin copolymers also are known. For example, Rajagopalan et al., U.S. Pat. No. 5,981,658 discloses making a golf ball having at least one layer formed by grafting an ethylenically unsaturated comonomer (functionalized olefin comonomer) onto a metallocene-catalyzed polymer (polyethylene) using a post-polymerization reaction process. The grafted polymer may be formed by admixing the metallocene-catalyzed polymer with a comonomer capable of bonding to the polymer and an organic peroxide, and mixing the admixture at a temperature greater than the melting point of the metallocene-catalyzed polymer for a time sufficient for the post-polymerization reaction to occur. For example, a maleic anhydride grafted ethylene-butene metallocene-catalyzed polymer may be made. In another embodiment, a maleic anhydride grafted ethylene-octene metallocene-catalyzed polymer may be made. The resulting golf balls have performance properties (compression, hardness, initial velocity) similar to golf balls made with ionomer covers according to the '658 patent.

Sullivan et al., U.S. Pat. No. 5,397,840 discloses a golf ball cover comprising a blend of non-ionic copolymers and ionic copolymers. The ionic and non-ionic copolymers are commercially available. The ionic copolymers are preferably sodium or zinc neutralized ethylene-acrylic acid copolymers. The non-ionized copolymer is preferably an ethylene-methacrylic acid copolymer or ethylene-acrylic acid copolymer. The resulting golf ball covers do not exhibit any decrease in durability or cut-resistance when compared to golf balls having pure ionomer covers according to the '840 patent.

As functionalized ethylene copolymers are formed, the polar functional groups are incorporated in alkyl chains pendant to the main polymer backbone. The functional groups may be grafted to the ethylene copolymer using techniques known in the art as described in U.S. Pat. Nos. 4,612,155; 4,762,890; 4,927,888; 4,950,541; 5,106,916; 5,180,788; 5,346,963; and 5,728,776. Alternatively, a comonomer having a functional group may be copolymerized with the ethylene comonomer using known methods such as high-temperature, high-pressure, free radical polymerization processes. Polymerization catalysts such as constrained geometry types as disclosed in U.S. Pat. No. 6,670,432 or Ziegler or Phillips type catalysts can be used. Metallocene-catalyzed copolymers also can be prepared following known techniques. Using conventional methods, the polymerized units having the functional groups are incorporated as alkyl side chains pendant to the main polymer backbone. These side chains or “branches” can have a short chain length or long chain length. One drawback with long side chains is the polymer structure may be disrupted and some of the desirable properties of the polyethylene backbone may be sacrificed. In other words, the long alkyl side chains that extend from the ethylene backbone may cause a loss in favorable polyethylene properties such as impact and tensile strength. This is particularly disadvantageous when the resulting polymer is used for materials in construction, automotive, or other industrial applications, where high mechanical strength is needed. In turn, the chemical industry has developed new methods for making functionalized ethylene copolymers having minimal side chain branching.

For example, Bieser et al., U.S. Pat. No. 6,214,924 discloses functionalized ethylene copolymers having a “linear structure” or “substantially linear structure.” Polymers with “linear structures” lack measurable or demonstrable long chain branches, that is, the polymer is substituted with an average of less than 0.01 long chain branch/1000 carbons. On the other hand, “substantially linear” polymers are characterized as having a backbone which is substituted with about 0.01 long chain branches/1000 carbons to about 3 long chain branches/1000 carbons, more preferably from about 0.01 long chain branches/1000 carbons to about 1 long chain branches/1000 carbons, and especially from about 0.05 long chain branches/1000 carbons to about 1 long chain branches/1000 carbons. Long chain branching is defined herein as a chain length of at least 6 carbons, above which the length cannot be distinguished using ¹³C nuclear magnetic resonance (NMR) spectroscopy. The long chain branch can be as long as about the same length as the length of the polymer backbone. In the '924 patent, the functionalized polyethylene is mixed with 5 to 70 weight percent of a homogenous ethylene α-olefin interpolymer and 30 to 95 weight percent of at least one filler, preferably calcium carbonate, barium sulfate, talc, silica/galls, alumina, or titanium dioxide. The final polyethylene composition has high tensile strength, indentation resistance, and filler-holding capacity and is especially useful for floor tile and sheeting applications according to the '924 patent.

Baugh, U.S. Pat. No. 7,504,465 discloses linear copolymers of ethylene and polar vinyl comonomers having randomly repeating —CH2-; —CH═CH— and units having polar functional substituents. The method involves copolymerizing a first polar substituted comonomer with a second non-polar unsubstituted comonomer in the presence of a Ru-based catalyst. The resulting functionalized polymers have longer run lengths, thus leading to higher crystallinites and melting points, and are substantially free from unfavorable polar clusters (for example, dyads and triads) and shorter run length sequences.

A golf ball made from a composition comprising a linear functionalized ethylene copolymer would be desirable. One objective of this invention is to develop such compositions so they can be used in different layers of a golf ball, for example, an outer core, intermediate layer, inner cover, and/or outer cover. The composition containing the linear functionalized ethylene copolymer should help provide the golf ball with an optimum combination of properties. Particularly, the resulting golf ball should have sufficient hardness and resiliency so that it shows good impact durability and flight distance when hit off a tee. At the same time, the ball should have a soft “feel” so that its flight path can be controlled on approach shots near the green. The present invention provides compositions that can be used to make such golf balls and the resulting golf balls.

SUMMARY OF THE INVENTION

The present invention provides golf balls containing having a core and at least one layer made from a functionalized ethylene copolymer having a linear or substantially linear structure. The copolymer is formed by copolymerizing an ethylene monomer with a comonomer having a functional group in the presence of a metal-based catalyst selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, and platinum. Preferably, a ruthenium-based catalyst is used. The core preferably comprises a rubber material such as polybutadiene. The functional comonomer may contain different functional groups such as, for example, acrylic acid, methacrylic acid, acrylates, methacrylates, maleic anhydride, maleic acid, maleate ester.

Ionomeric and non-ionomeric functionalized ethylene copolymers may be prepared. For example, the copolymer may contain acrylic or methacrylic acid groups that are neutralized to less than or greater than 70% by a cation source. In other instances, the copolymer may contain maleic anhydride, maleic acid, or maleate ester groups that are neutralized to less than or greater than 70% by a cation source. Preferred cation sources are metal cations and salts thereof, wherein the metal is preferably lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, manganese, nickel, chromium, copper, or a combination thereof. A metal stearate (for example, zinc stearate) or other metal fatty acid salt may be used. In addition, melt flow modifiers such as fatty acids and salts thereof may be added.

The functionalized ethylene copolymer may further comprise an α-olefin comonomer having 3 to 20 carbon atoms. For example, the optional α-olefin comonomer may be selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. The functionalized ethylene copolymers of this invention may be used in various ball constructions. Golf balls having improved mechanical strength, weatherability, thermal stability, durability, and impact and tensile strength, and other favorable properties may be made with these compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the present invention are set forth in the appended claims. However, the preferred embodiments of the invention, together with further objects and attendant advantages, are best understood by reference to the following detailed description in connection with the accompanying drawings in which:

FIG. 1 is a front view of a dimpled golf ball made in accordance with the present invention;

FIG. 2 is cross-sectional view of a two-piece golf ball having a cover made of a functionalized ethylene copolymer in accordance with the present invention;

FIG. 3 is a cross-sectional view of a multi-layered (three-piece) golf ball having an intermediate layer made of a functionalized ethylene copolymer composition in accordance with the present invention;

FIG. 4 is a cross-sectional view of a multi-layered (four-piece) golf ball having an inner cover layer made of a functionalized ethylene copolymer composition in accordance with the present invention;

FIG. 5 is a cross-sectional view of a multi-layered (four-piece) golf ball having an intermediate layer made of a functionalized ethylene copolymer composition in accordance with the present invention; and

FIG. 6 is a cross-sectional view of a multi-layered (four-piece) golf ball having an outer core layer made of a functionalized ethylene copolymer composition in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates generally to golf balls containing at least one “layer” made from an ethylene copolymer that has been functionalized. The term, “layer” as used herein means generally any spherical portion of a golf ball. The functionalized ethylene copolymer composition of this invention may be used to form any layer in the golf ball structure including, but not limited to, an outer cover, inner cover, intermediate layer, and/or outer core layer.

Functionalized Ethylene Copolymers

The term, “copolymer” as used herein is meant to include copolymers formed by polymerizing two comonomers together, terpolymers that are formed by polymerizing three comonomers together, and products that are formed by polymerizing more than three comonomers together. The term, “non-ionomeric copolymers” as used herein is meant to include copolymers other than ionomeric copolymers, which generally refer to olefin copolymers formed by polymerizing olefins with a vinyl comonomer having an acid group such as methacrylic or acrylic acid and partially or fully neutralized with salts of sodium, lithium, zinc, and magnesium, and the like.

The functionalized copolymer in the compositions used to prepare the layer(s) of the golf ball of this invention is an ethylene copolymer comprising ethylene and at least one functional comonomer having at least one functional group. Preferably, the ethylene content is at least about 50% by weight of the total comonomers making up the copolymer. More preferably, the ethylene content is in the range of about 50% to about 99% by weight of the total comonomers comprising the copolymer. The functionalized copolymer may further comprise an α-olefin comonomer(s), which is copolymerized with the ethylene and functional comonomer. Preferably, the α-olefin comonomer(s) contains from 3 to about 20 carbon atoms. Examples of α-olefin comonomers that may be used in accordance with this invention are propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadecene and the like. Preferably, the α-olefin comonomer has 3 to 10 carbons.

The functional comonomer may contain any suitable functional group. For example, the functional group may be selected from a group consisting of sulfonic acid, sulfonic acid derivatives, chlorosulfonic acid, vinyl ethers, vinyl esters, primary amines, secondary amines, tertiary amines, mono-carboxylic acids, dicarboxylic acids, partially or fully ester derivatized mono-carboxylic acids, partially or fully ester derivatized dicarboxylic acids, anhydrides of dicarboxylic acids, cyclic imides of dicarboxylic acids, and ionomeric derivatives thereof. Particularly, acids such as maleic acid, fumaric acid, himic acid, itaconic acid, citraconic acid, mesaconic acid, acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, and acid anhydrides such as maleic anhydride and himic anhydride may be used. More particularly, carboxylic acids such as acrylic and methacrylic acid; carboxylic acid esters such as methyl, ethyl, or butyl acrylate and methyl, ethyl, or butyl methacrylate; and acid anhydrides such as maleic anhydride may be used. It should be recognized that mixtures of functional groups also may be used. The functional group is used so that the functionalized ethylene copolymer will contain from about 0.01 to about 35% by weight of functional group, based on total weight of functionalized ethylene copolymer. Some examples of functionalized polyethylene copolymers that can be made in accordance with this invention include ethylene/vinyl acetate (EVA), ethylene/acrylic acid (EAA), ethylene/methacrylic acid (EMAA), and ethylene/maleic anhydride (EMAH) as well as ionomers thereof.

In the present invention, it is important that the functionalized ethylene copolymer has a “linear” or “substantially linear” structure as discussed further below. By the term, “linear” as used herein, it is meant functionalized ethylene copolymers characterized as lacking measurable or demonstrable long chain carbon branches pendant from the main polymer backbone. By the term, “structurally linear” as used herein, it is meant functionalized ethylene copolymers characterized as having a backbone which is substituted with about 0.01 long chain branches/1000 carbons to about 3 long chain branches/1000 carbons, more preferably from about 0.01 long chain branches/1000 carbons to about 1 long chain branches/1000 carbons, and especially from about 0.05 long chain branches/1000 carbons to about 1 long chain branches/1000 carbons. Long chain branching is defined herein as a chain length of at least 6 carbons, above which the length cannot be distinguished using ¹³C nuclear magnetic resonance (NMR) spectroscopy. The long chain branch can be as long as about the same length as the length of the polymer backbone. Long chain branching may be determined by ¹³C NMR spectroscopy and is quantified using the method of Randall (Rev. Macromol. Chem. Phys., C29 (2&3), p. 285-297), the disclosure of which is incorporated herein by reference.

The functionalized ethylene copolymer having the linear or substantially linear structure is produced by copolymerizing a comonomer having a functional group with an ethylene monomer in the presence of a metal-based catalyst. Preferably, the metal-based catalyst is selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, and platinum. More preferably, a ruthenium-based catalyst is used, as disclosed in Baugh et al., U.S. Pat. No. 7,504,465, the disclosure of which is hereby incorporated by reference. This copolymerizing step is conducted so the ratio of the polar-substituted functional comonomer to the non-polar unsubstituted ethylene comonomer is such that the units having polar functional substituents in the main chain of the functionalized ethylene copolymer comprise an amount no greater than about 20 mole %, preferably 15 mole %, and most preferably 10 mole %, of the total number of the units therein on a methylene or C₂ basis. In another embodiment, the copolymerizing step is conducted so the ratio of the polar-substituted functional comonomer to the non-polar unsubstituted ethylene comonomer is such that the units having polar functional substituents in the main chain of the functionalized ethylene copolymer comprise an amount no greater than about 35 weight %, preferably no greater than 30 weight %, more preferably no greater than 25 weight %, and most preferably 15 to 20 weight %, of the total number of the units therein on a methylene or C₂ basis. Particularly, the Ru-based catalyst has the following structural formula:

wherein L₁ and L₂ are independently selected from the group consisting of alkyl phosphine, aryl phosphine, 1,3-dimesitylimidazol-2-ylidene, 1,3-di(2,6-diisopropylphenyl)imidazol-2-ylidene, 1,3-diarylimidazol-2-ylidene, 1,3-dimesitylimidazolidin-2-ylidene, 1,3-di(2,6-diisopropylphenyl)imidazolidin-2-ylidene, 1,3-diphenyltriazine, and pyridine; L₃, if present, is pyridine and is identical to L₂; and R₄ is selected from the group consisting of hydrogen, C₁-C₂₀ linear alkyl, C₁-C₂₀ branched alkyl, C₁-C₂₀ cycloalkyl, C₁-C₂₀ alkenyl, aryl and phenyl.

Functionalized ethylene terpolymers having softening polymeric units also may be produced in accordance with this invention. That is, the ethylene monomer may be copolymerized with a functionalized comonomer and an optional additional comonomer to form a terpolymer of ethylene, functional comonomer, and optionally other monomer(s). The optional softening comonomer may be selected from the group consisting of vinyl esters of aliphatic carboxylic acids wherein the acids have 2 to 10 carbon atoms, vinyl ethers wherein the alkyl groups contains 1 to 10 carbon atoms, and alkyl acrylates or methacrylates wherein the alkyl group contains 1 to 10 carbon atoms. Suitable softening comonomers include, for example, vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, and the like.

The functionalized ethylene copolymer of this invention may be ionic or non-ionic. For example, an ionic functionalized copolymer of ethylene and a comonomer having a carboxylic acid group such as methacrylic, acrylic, crotonic, maleic, fumaric, or itaconic acid may be produced in accordance with this invention. As discussed above, the copolymer may optionally include a softening comonomer. If an ionic functionalized ethylene copolymer is prepared, it preferably has an acid content in the range of about 1 to about 30 wt. %, more preferably from 5 to 20 wt. %. “Low acid” and “high acid” ionic functionalized ethylene copolymers, as well as blends thereof, may be used. In general, low acid ionomers are defined as containing 16 weight percent or less of a carboxylic acid, whereas high acid ionomers are defined as containing greater than 16 weight percent of a carboxylic acid. The carboxylic acid groups of the copolymer may be partially neutralized (particularly, about 10 to about 75 wt. %, and more particularly, 30 to wt. 70% of the acid is neutralized), highly neutralized (particularly, about 75 to about 98 wt. %), or highly neutralized (particularly, about 98 to about 100 wt. %) with a suitable cation source, such as metal cations and salts thereof, organic amine compounds, ammonium, sodium hydroxide, bases, and combinations thereof. Preferred cation sources are metal cations and salts thereof, wherein the metal is preferably lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, manganese, nickel, chromium, copper, or a combination thereof. A metal stearate (for example, zinc stearate) or other metal fatty acid salt may be used. In addition, melt flow modifiers such as, for example, fatty acids and salts thereof, polyamides, polyesters, polyacrylates, polyurethanes, polyethers, polyureas, polyhydric alcohols, and combinations thereof may be added. The metal cation used to neutralize the acid groups may be the same or different metal used in the above-discussed catalyst complex for the reaction that produces the functionalized polyethylene. Preferably, the metal cation used to neutralize the acid groups is different than the metal used in the catalyst complex.

The functionalized ethylene copolymer compositions used to produce the layer(s) of the golf ball of this invention have many advantageous physical properties and features. For example, the flexural modulus (as measured in accordance with ASTM D-790) of the functionalized ethylene copolymer composition is generally about 10 to about 100 kpsi, preferably 20 to 80 kpsi, and more preferably 30 to 75 kpsi. The material hardness (as measured per the test methods described further below) of the functionalized ethylene copolymer composition is about 25 to about 75 Shore D, preferably 30 to 70 Shore D, and more preferably 35 to 65 Shore D. In addition, the composition has an elongation at break (as measured in accordance with ASTM D-638) of about 100 to about 400%, preferably 150 to 300%, and more preferably 150 to 275%; a tensile strength at break (as measured in accordance with ASTM D-638) of about 1 to about 7 kpsi, preferably 2 to 6 kpsi, and more preferably 3 to 5 kpsi; and a notched Izod strength (as measured in accordance with ASTM D-256) of at least 10, preferably 15 to no break, and more preferably 20 to no break as measured at 23° C. The Vicat softening temperature (as measured in accordance with ASTM D-1525-70) of the composition is about 50 to about 100° C., preferably 55 to 95° C., and more preferably 60 to 90° C. Lastly, the density (as measured in accordance with ASTM D-792) of the composition is about 0.8 to about 1.0, preferably 0.85 to 0.97, and more preferably 0.9 to 0.95.

Core

The core of the golf ball may be solid, semi-solid, fluid-filled, or hollow, and the core may have a single-piece or multi-piece structure. A variety of materials may be used to make the core including thermoset compositions such as natural and synthetic rubbers, styrene butadiene, polybutadiene, poly(cis-isoprene), poly(trans-isoprene), thermoplastics such as ionomer resins, polyamides or polyesters; and thermoplastic and thermoset polyurethane and polyurea elastomers. In one embodiment, the core is a single-piece structure made from polybutadiene. In other instances, a multi-piece core is constructed; that is, there are two or more core pieces or layers. For example, an inner core may be made of a first base rubber material and an outer core layer, surrounding the inner core, may be made of a second base rubber material. The first and second base rubbers of the respective core layers may be the same or different materials. For example, in one version, each core layer may be made of polybutadiene rubber. In another version, the inner core may be made of polybutadiene rubber and the outer core may be made of polyisoprene rubber.

Preferably, the composition used to make the core contains a base rubber, a cross-linking agent, a filler, an initiator agent, and a cis-to-trans converting material (for example, organosulfur or inorganic sulfur compounds). Typical base rubber materials include natural and synthetic rubbers such as, for example, polybutadiene, styrene-butadiene, and polyisoprene. In one embodiment, the base rubber is 1,4-polybutadiene having a cis-structure of at least forty percent (40%). The polybutadiene can be blended with other elastomers such as natural rubber, polyisoprene rubber, styrene-butadiene rubber and/or other polybutadienes. Another suitable rubber that may be used in the core is trans-polybutadiene. This polybutadiene isomer is formed by converting the cis-isomer of the polybutadiene to the trans-isomer during a molding cycle. A soft and fast agent such as pentachlorothiophenol (PCTP) or ZnPCTP may be blended with the polybutadiene. These compounds also may function as a cis-to-trans catalyst to convert some cis-1,4 bonds in the polybutadiene into trans-1,4 bonds.

The cross-linking agent in the core composition typically includes a metal salt such as a zinc salt or magnesium salt, of an acid having from 3 to 8 carbon atoms, such as (meth)acrylic acid. Suitable cross-linking agents include metal salt diacrylates, dimethacrylates and monomethacrylates, wherein the metal is magnesium, calcium, zinc, aluminum, sodium, lithium or nickel. The initiator agent can be any known polymerization initiator which decomposes during the curing cycle including, but not limited to, dicumyl peroxide, 1,1-di-(t-butylperoxy)3,3,5-trimethyl cyclohexane, a-a bis-(t-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5 di-(t-butylperoxy)hexane or di-t-butyl peroxide, and mixtures thereof. Fillers, which may be used to modify such properties as the specific gravity, density, hardness, weight, modulus, resiliency, compression, and the like may be added to the base rubber composition. Normally, the fillers are inorganic, and suitable fillers include numerous metals or metal oxides, such as zinc oxide and tin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay, tungsten, tungsten carbide, silica, and mixtures thereof. Fillers may also include various foaming agents or blowing agents, zinc carbonate, regrind (recycled core material typically ground to about 30 mesh or less particle size), high-Mooney-viscosity rubber regrind, and the like. In addition, polymeric, ceramic, metal, and glass microspheres may be used. Suitable types and amounts of base rubber, cross-linking agents, fillers, and initiator agents used for making the core composition are known in the art.

Golf balls made in accordance with this invention can be of any size, although the USGA requires that golf balls used in competition have a diameter of at least 1.68 inches and a weight of no greater than 1.62 ounces. For play outside of USGA competition, the golf balls can have smaller diameters and be heavier. For example, the diameter of the golf ball may be in the range of about 1.68 to about 1.80 inches. In one embodiment, the core is a single-piece having an outside diameter of about 1.00 to about 1.65 inches. Preferably, the single-piece core has a diameter of about 1.50 to about 1.64 inches. The core generally makes up a substantial portion of the ball, for example, the core may constitute at least about 90% of the ball. The hardness of the core may vary depending upon desired properties of the ball. In general, core hardness is in the range of about 30 to about 90 Shore D and more preferably in the range of about 35 to about 60 Shore D. The compression of the core is generally in the range of about 40 to about 110 and more preferably in the range of about 70 to about 100. In general, when the ball contains a relatively soft core, the resulting spin rate of the ball is relatively low. On the other hand, when the ball contains a relatively hard core, the resulting spin rate of the ball is relatively high.

As mentioned above, in another embodiment, the core may include two or more core layers or pieces. The outer core layer surrounds and encapsulates the inner core. This structure may be referred to as a multi-layered core or two-piece core. The inner core may be made of a first base rubber material and the outer core layer, surrounding the inner core, may be made of a second base rubber material. The respective core layers may be made of the same or different base rubbers, and various cross-linking agents, fillers, and initiator agents may be added to the rubber compositions as described above. The inner core and outer core layer, together, may be referred to as the “center” of the ball. In such balls having two-piece cores, the inner core may have a diameter of about 0.50 to about 1.30 inches, more preferably 1.00 to 1.15 inches, and be relatively soft (that is, it may have a compression of less than about 30.) Meanwhile, the encapsulating outer core layer may have a thickness of about 0.20 to about 0.60 inches and be relatively hard (compression of about 70 or greater.) That is, the two-piece core or “center” of the ball, which constitutes the inner core and outer core layer may have a total diameter of about 1.50 to about 1.64 inches, more preferably 1.510 to 1.620 inches, and a compression of about 80 to about 115, more preferably 85 to 110. The polymers, free-radical initiators, filler, cross-linking agents, and other ingredients may be mixed together to form the single-piece or multi-piece core using conventional techniques. Particularly, a compression or injection-molding process may be used to form the spherical cores.

Cover Material

The functionalized ethylene compositions of this invention may be used with any type of ball construction known in the art. Such golf ball designs include, for example, single-piece, two-piece, three-piece, and four-piece designs. The core, intermediate (casing), and cover portions making up the golf ball each can be single or multi-layered depending upon the desired playing performance properties. That is, the composition of this invention may be used in a core, intermediate layer, and/or cover and each of these pieces may have a single or multiple layers. In FIG. 1, one version of a golf ball that can be made in accordance with this invention is generally indicated at (10). Various patterns and geometric shapes of dimples (11) can be used to modify the aerodynamic properties of the golf ball (10). The dimples (11) can be arranged on the surface of the ball (10) using any suitable method known in the art. Referring to FIG. 2, a two-piece golf ball (12) having a solid core (14) and cover (16) made of the functionalized ethylene compositions of this invention is shown.

In another embodiment, as shown in FIG. 3, the golf ball (20) includes an intermediate layer (22) disposed between the inner core (24) and outer cover (25). As used herein, the term, “intermediate layer” means a layer of the ball disposed between the core and cover. The intermediate layer may be considered an outer core layer, or inner cover layer, or any other layer disposed between the inner core and outer cover of the ball. The intermediate layer also may be referred to as a casing or mantle layer. It also should be understood that the ball may include one or more intermediate layers.

The intermediate layer may be made of a variety of materials. In one preferred embodiment, the intermediate layer (22) is made of functionalized ethylene copolymer composition, while the cover (25) is made of a different polymer composition as illustrated in FIG. 3. In the golf ball (20) of FIG. 3, the cover (25) may be made of conventional thermoplastic or thermoset resins. Suitable resins that may be used to construct the cover (25) include, but are not limited to, ionomer resins (for example, Surly® ionomer resins and DuPont® HPF 1000 and HPF 2000, commercially available from E. I. du Pont de Nemours and Company; Iotek® ionomers, commercially available from ExxonMobil Chemical Company; Amplify® IO ionomers of ethylene acrylic acid copolymers, commercially available from The Dow Chemical Company; and Clarix® ionomer resins, commercially available from A. Schulman Inc.); polyurethanes; polyureas; copolymers and hybrids of polyurethane and polyurea; polyethylene, including, for example, low density polyethylene, linear low density polyethylene, and high density polyethylene; polypropylene; rubber-toughened olefin polymers; acid copolymers, for example, poly(meth)acrylic acid, which do not become part of an ionomeric copolymer; plastomers; flexomers; styrene/butadiene/styrene block copolymers; styrene/ethylene-butylene/styrene block copolymers; dynamically vulcanized elastomers; copolymers of ethylene and vinyl acetates; copolymers of ethylene and methyl acrylates; polyvinyl chloride resins; polyamides, poly(amide-ester) elastomers, and graft copolymers of ionomer and polyamide including, for example, Pebax® thermoplastic polyether block amides, commercially available from Arkema Inc; cross-linked trans-polyisoprene and blends thereof; polyester-based thermoplastic elastomers, such as Hytrel®, commercially available from E. I. du Pont de Nemours and Company; polyurethane-based thermoplastic elastomers, such as Elastollan®, commercially available from BASF; synthetic or natural vulcanized rubber; and combinations thereof. In a particular embodiment, the cover (25) is a single layer formed from a composition selected from the group consisting of ionomers, polyester elastomers, polyamide elastomers, and combinations of two or more thereof.

Polyurethanes, polyureas, and polyurethane/polyurea hybrids are also particularly suitable for forming cover layers. When used as cover layer materials, polyurethanes and polyureas can be thermoset or thermoplastic. Thermoset materials can be formed into golf ball layers by conventional casting or reaction injection molding techniques. Thermoplastic materials can be formed into golf ball layers by conventional compression or injection molding techniques.

Suitable polyurethanes are further disclosed, for example, in U.S. Pat. Nos. 5,334,673; 6,476,176; 6,506,851; 6,867,279; 6,960,630; and 7,105,623, the disclosures of which are hereby incorporated herein by reference. Suitable polyureas are further disclosed, for example, in U.S. Pat. Nos. 5,484,870; 6,835,794; and 6,964,621, the disclosures of which are hereby incorporated herein by reference. Suitable polyurethane/polyurea cover materials include polyurethane/polyurea blends and hybrids and copolymers comprising urethane and urea segments, as disclosed in U.S. Pat. Nos. 7,041,769 and 7,186,777, the disclosures of which are hereby incorporated herein by reference. As is customary, the cover compositions may include additional materials such as catalysts, coloring agents, optical brighteners, whitening agents, pigments, dyes, cross-linking agents, UV light absorbers, light stabilizers, antioxidants, defoaming agents, processing aids, release agents, wetting agents, plasticizers, surfactants, compatibility agents, blowing agents, foaming agents, reinforcing agents, density-adjusting fillers, and the like.

Intermediate Layer

As discussed above and shown in FIG. 3, in one embodiment, the golf ball (20) may include an intermediate layer (22) made of the functionalized ethylene copolymer composition of this invention. When the functionalized ethylene copolymer composition is used, the intermediate layer has good properties, particularly higher flex modulus, higher resiliency or coefficient of restitution (COR), good impact-resistance and durability, and good moisture vapor-resistance. The moisture vapor transmission rate (MVTR) of the intermediate layer is an important property. As discussed above, the inner core primarily provides resiliency to the golf ball. As the core absorbs water, it tends to lose its resiliency. The compression and COR of the ball may be reduced significantly if a large amount of water vapor permeates into the core. The intermediate layers of the balls in this invention help minimize moisture penetration into the core. Preferably, the moisture vapor barrier layer, comprising the functionalized ethylene copolymer composition has a moisture vapor transmission rate less than the about 4.0 grams·mm/m²·day, more preferably less than 3 grams·mm/m²·day, and most preferably less than 1.0 grams·mm/m²·day, particularly 0.5 to 1.0 grams·mm/m²·day. The moisture vapor transmission rate is defined as the mass of moisture vapor that diffuses into a material of a given thickness per unit area per unit time. The preferred standards of measuring the moisture vapor transmission rate include ASTM F1249-90 entitled “Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor,” ASTM F372-94 entitled “Standard Test Method for Water Vapor Transmission Rate of Flexible Barrier Materials Using an Infrared Detection Technique,” and ASTM D-96 entitled “Water Vapor Transmission Rate” among others.

Referring now to FIG. 4, another version of a golf ball (28) made in accordance with this invention is shown. Here, the ball (28) contains a multi-layered cover having an inner cover layer (29) and outer cover layer (30). In the version shown in FIG. 4, the inner cover layer (29) is made of the functionalized ethylene copolymer composition of this invention, while the intermediate layer (34) is made of a conventional resin material. The resin constituting the intermediate layer (34) may be selected from a variety of thermoplastic and thermosetting materials.

Suitable thermoplastic compositions for making the intermediate layer (34) in golf ball (28) include, but are not limited to, partially- and fully-neutralized ionomers as described above. Alternatively, non-ionomeric polymers including the following may be used: polyesters; polyamides; polyamide-ethers, and polyamide-esters; polyurethanes, polyureas, and polyurethane-polyurea hybrids; fluoropolymers; metallocene-catalyzed polymers; polystyrenes; polypropylenes and polyethylenes; polyvinyl chlorides and grafted polyvinyl chlorides; polyvinyl acetates; polycarbonates including polycarbonate/acrylonitrile-butadiene-styrene blends, polycarbonate/polyurethane blends, and polycarbonate/polyester blends; polyvinyl alcohols; polyethers; polyimides, polyetherketones, polyamideimides; and mixtures of any two or more of the above thermoplastic polymers. Meanwhile, the outer cover layer (30) of the golf ball (28) shown in FIG. 4 may be made using the above-described cover materials.

Ball Construction

The functionalized ethylene copolymers of this invention may be used with any type of ball construction known in the art. Such golf ball designs include, for example, single-piece, two-piece, three-piece, and four-piece designs so long as at least one layer comprises a functionalized ethylene copolymer composition prepared in accordance with this invention. The core, intermediate, and/or cover materials may be single or multi-layered.

The functionalized ethylene copolymer composition constituting the layer(s) of the golf ball may contain additives, ingredients, and other materials in amounts that do not detract from the properties of the final composition. These additive materials include, but are not limited to, activators such as calcium or magnesium oxide; fatty acids such as stearic acid and salts thereof; fillers and reinforcing agents such as organic or inorganic particles, for example, clays, talc, calcium, magnesium carbonate, silica, aluminum silicates zeolites, powdered metals, and organic or inorganic fibers, plasticizers such as dialkyl esters of dicarboxylic acids; surfactants; softeners; tackifiers; waxes; ultraviolet (UV) light absorbers and stabilizers; antioxidants; optical brighteners; whitening agents such as titanium dioxide and zinc oxide; dyes and pigments; processing aids; release agents; and wetting agents.

The functionalized ethylene copolymer composition used in the layers of the golf balls of this invention may be blended with non-ionomeric polymers such as, for example, vinyl resins, polyolefins including those produced using a single-site catalyst or a metallocene catalyst, polyurethanes, polyureas, polyamides, polyphenylenes, polycarbonates, polyesters, polyacrylates, engineering thermoplastics, and the like. The functionalized ethylene copolymer also may be blended with ionomeric resins.

As discussed above, ionomeric resins generally refer to ionic copolymers of an olefin, such as ethylene, and an unsaturated carboxylic acid, such as methacrylic acid, acrylic acid, or maleic acid. Other possible carboxylic acid groups include crotonic, maleic, fumaric, and itaconic acid. Low acid and high acid ionomers, as defined above, as well as blends of such ionomers, may be used. The acidic group in the ionic copolymer is partially or totally neutralized with metal ions such as zinc, sodium, lithium, magnesium, potassium, calcium, manganese, nickel, chromium, copper, or a combination thereof. For example, ionomeric resins having carboxylic acid groups that are neutralized from about 10 percent to about 100 percent may be used. That is, the acid groups of the ionomers may be partially, highly, or fully-neutralized. Blends of ionomers may be prepared. The blend may contain about 10 to about 90% by weight of the functionalized ethylene ionomeric copolymer and about 90 to about 10% by weight of a different partially, highly, or fully-neutralized ionomeric copolymer. In particular embodiments, the concentration of the functionalized ethylene ionomeric copolymer may be about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%; and the concentration of the other partially, highly, or fully-neutralized ionomeric copolymer may be about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% or 10%, respectively. For instance, the polymer matrix may be made of: a) a composition comprising a blend of a first high acid functionalized ethylene ionomeric copolymer of this invention and a different, second low acid neutralized ionomeric copolymer, wherein the first high acid ionomer is neutralized with the same or different cation used to neutralize the second low acid ionomer; or b) a composition comprising a blend of a first low acid functionalized ethylene ionomeric copolymer of this invention and a different, second high acid neutralized ionomeric copolymer, wherein the first low acid ionomer is neutralized with the same or different cation used to neutralize the second high acid ionomer; or c) a composition comprising a blend of a first high acid functionalized ethylene ionomeric copolymer of this invention and a different, second high acid ionomer, wherein the first high acid ionomer is neutralized with the same or different cation used to neutralize the second high acid ionomer; or d) a composition comprising a blend of a first low acid fanctionalized ethylene ionomeric copolymer of this invention and a different, second low acid ionomer, wherein the first low acid ionomer is neutralized with the same or different cation used to neutralize the second low acid ionomer.

In one version, the polymer matrix constituting the ball layer consists of 100% by weight of the functionalized ethylene copolymer of this invention. In another version, the polymer matrix constituting the ball layer is a blend of the functionalized ethylene copolymer and non-functionalized ethylene copolymer such as an ethylene-butene copolymer. The functionalized and non-functionalized ethylene copolymers are compatible with each other and form a homogenous blend on a macroscopic scale. The blend may contain about 10 to about 90% by weight of the functionalized ethylene copolymer and about 90 to about 10% by weight of the non-functionalized ethylene copolymer. In particular embodiments, the concentration of the functionalized ethylene copolymer may be about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%, and the concentration of the counterpart non-fanctionalized ethylene copolymer may be about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% or 10%, respectively.

In yet another version, the polymer matrix constituting the ball layer is a blend of the functionalized ethylene copolymer with another polymer. For instance, the blend may contain about 10 to about 90% by weight of the functionalized ethylene copolymer and about 90 to about 10% by weight of another polymer such as, for example, vinyl resins, polyolefins, polyamides, polycarbonates, polyesters, polyacrylates. partially- or fully-neutralized ionomeric acid copolymers, non-ionomeric acid copolymers, engineering thermoplastics, fatty acid/salt-based highly neutralized polymers, polybutadienes, polyurethanes, polyureas, polyesters, polycarbonate/polyester blends, thermoplastic elastomers, and the like. In particular embodiments, the concentration of the functionalized ethylene copolymer may be about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%, and the concentration of the counterpart polymer may be about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% or 10%, respectively.

The golf balls of the present invention preferably have a “coefficient of restitution” (“COR”) of at least 0.750 and more preferably at least 0.800 (as measured per the test methods below) and a compression of from about 70 to about 110, preferably from 90 to 100 (as measured per the test methods below).

The compression value of a golf ball or a golf ball subassembly (for example, golf ball core) is an important property affecting the ball's playing performance. For example, the compression of the core can affect the ball's spin rate off the driver as well as the “feel” of the ball as the club face makes impact with the ball. In general, balls with relatively low compression values have a softer feel. As disclosed in Jeff Dalton's Compression by Any Other Name, Science and Golf IV, Proceedings of the World Scientific Congress of Golf (Eric Thain ed., Routledge, 2002) (“J. Dalton”) several different methods can be used to measure compression including Atti compression, Riehle compression, load/deflection measurements at a variety of fixed loads and offsets, and effective modulus. For purposes of the present invention, “compression” refers to Atti compression and is measured according to a known procedure, using an Atti compression device, wherein a piston is used to compress a ball against a spring. The test methods for measuring compression of the ball are described in further detail below.

The “coefficient of restitution” or “COR” of a golf ball means the ratio of a ball's rebound velocity to its initial incoming velocity when the ball is fired out of an air cannon into a rigid vertical plate. The COR for a golf ball is written as a decimal value between zero and one. A golf ball may have different COR values at different initial velocities. The United States Golf Association (USGA) sets limits on the initial velocity of the ball so one objective of golf ball manufacturers is to maximize the COR under these conditions. Balls with a higher rebound velocity have a higher COR value. Such golf balls rebound faster, retain more total energy when struck with a club, and have longer flight distance. In general, the COR of the ball will increase as the hardness of the ball is increased. The test methods for measuring the COR of the ball are described in further detail below.

In one embodiment, as shown in FIG. 2, a two-piece golf ball (12) having a solid core (14) and an overlying cover layer (16) is provided. As discussed above, the core (14) is made of a polybutadiene rubber or other suitable material and the cover layer (16) is made of the ethylene copolymer composition in accordance with this invention. The thickness of the cover layer (16) may vary, but it is generally in the range of about 0.030 to about 0.075 inches and more preferably about 0.035 to about 0.065 inches. The surface hardness of the cover layer (16) is generally in the range of about 30 to about 68 Shore D and more preferably about 45 to about 65 Shore D. The single-piece core (14) has a diameter of about 1.58 inches. The surface hardness of the core (14) may vary depending upon the desired properties of the ball (12). In general, the core has a surface hardness is in the range of about 30 to about 65 Shore D and more preferably in the range of about 35 to about 60 Shore D. The compression of the core is preferably in the range of about 30 to about 90 and more preferably about 40 to about 85. The core (14) generally makes up a substantial portion of the ball (12), for example, the core (14) may constitute at least 95% or greater of the ball structure. The core (14) preferably has a surface hardness in the range of about 20 to about 55 Shore D; more preferably about 25 to about 50 Shore D; and most preferably about 30 about 45 Shore D. The elasticity modulus of the core (14) preferably is in the range of about 2 to about 35 kpsi; more preferably about 5 to about 25 kpsi; and most preferably about 10 to about 20 kpsi.

Referring to FIG. 3, another version of a golf ball (20) is shown. The ball (20) includes an inner core (24), an outer cover layer (25), and an intermediate layer (22) disposed between the core (24) and cover (25), wherein the intermediate layer (22) is made from the functionalized ethylene copolymer composition of this invention. The core (24) is made of polybutadiene rubber or other suitable material as described above and has a diameter in the range of about 1.30 to about 1.60 inches. The cover layer (25) is made of a thermoplastic composition or thermoset composition as described above. The range of thickness for the intermediate layer (22) may vary, but it generally has a thickness of 0.010 to 0.030 inches, preferably 0.015 to 0.025 inches, and more preferably about 0.1015 to 0.020 inches. The intermediate layer (22) preferably has a Shore D material hardness of 50 to 75, preferably 55 to 68, and most preferably 60 to 65.

In another embodiment, as shown in FIG. 4, a four-piece golf ball (28) having a solid core (32), an intermediate layer (34), and multi-layered cover constituting an inner cover layer (29) and outer cover layer (30) is provided. In this version, the core (32) is made of polybutadiene rubber or other suitable material, and the intermediate layer (24) is made of an ionomer resin or other suitable material as described above. The intermediate layer (24) has a thickness in the range of about 0.010 to about 0.030 inches and a material hardness in the range of about 40 to about 70, preferably about 50 to about 65, and most preferably about 55 to about 63 Shore D. In this particular version of the golf ball (28), the inner cover layer (29) is made of the functionalized ethylene copolymer composition per this invention. The inner cover layer (29) has a thickness of about 0.02 to about 0.50 inches and Shore D material hardness of about 50 to about 70. The outer cover layer (30), which surrounds the inner cover layer (29), may be made of a thermoplastic or thermoset composition. For example, the outer cover (30) may be made of polyurethane, polyurea, ionomer resin or any of the other cover materials discussed above. The outer cover layer (30) generally has a thickness in the range of about 0.020 to about 0.035 inches and a Shore D material hardness in the range of about 45 to about 65.

In yet another embodiment, as shown in FIG. 5, a four-piece golf ball (40) having a solid core (42), an intermediate layer (44), and multi-layered cover constituting an inner cover layer (45) and outer cover layer (46) is provided. In this version, the core (42) is made of polybutadiene rubber or other suitable material, and the intermediate layer (44) is made of a functionalized ethylene copolymer composition. The inner (45) and outer (46) cover layers may be made of any suitable cover material such as, for example, polyurethane, polyurea, or ionomer resin.

Referring to FIG. 6, another embodiment of the golf ball (48) of this invention is shown. The golf ball (48) illustrated in FIG. 6 contains a two-piece core; that is, there are two core pieces. The inner core (49) may be made of a first base rubber material and the outer core layer (50), which surrounds the inner core (49), may be made of a second base rubber material. The respective core pieces (49, 50) may be made of the same or different rubber materials as described above. In a preferred version, as shown in FIG. 6, the inner core segment (49) is made of polybutadiene while the outer core layer (50) is made of the functionalized ethylene copolymer composition in accordance with this invention. It should be understood that the golf ball constructions shown in FIGS. 1-6 are for illustrative purposes only and not meant to be restrictive. A wide variety of golf ball constructions may be made in accordance with the present invention depending upon the desired properties of the ball so long as at least one layer contains the functionalized ethylene composition of this invention. As discussed above, such constructions include, but are not limited to, single-piece, two-piece, three-piece, and/or four-piece designs. For example, the balls may have single or multi-piece cores and the cores, intermediate layers, and/or covers may be single or multi-layered.

The golf balls of this invention may be constructed using any suitable technique known in the art. These methods generally include compression molding, flip molding, injection molding, retractable pin injection molding, reaction injection molding (RIM), liquid injection molding (LIM), casting, vacuum forming, powder coating, flow coating, spin coating, dipping, spraying, and the like.

The functionalized ethylene copolymer compositions of this invention should provide the golf ball with advantageous properties and features. Because the functionalized ethylene copolymers have a linear or substantially linear structure, the copolymers include properties of both the polar functional groups and non-polar ethylene polymer backbone. In other words, the linear and substantially linear functionalized ethylene copolymers used to form the golf ball layers possess the benefits of the pendant functional groups as well as the ethylene backbone. There is no long side chain branching that will interfere with the polymer structure. The polar functional groups may provide improved adhesion, dyeability, printability, solvent-resistance, weatherability, thermal stability, melt-strength, and the like. The ethylene backbone may provide high impact and tensile strength. Compositions containing the linear and substantially linear functionalized ethylene copolymers, which have been developed in accordance with this invention, can be used in various ball constructions to provide desirable playing performance properties. For example, the compositions may be used to make the outer core, intermediate layer, inner cover, and/or outer cover. As discussed above, compositions containing blends of the functionalized ethylene copolymers with ionomeric or non-ionomeric materials are particularly advantageous. The resulting golf ball has sufficient hardness and good impact durability. The ball has improved resiliency so that it shows good flight distance when hit off a tee. At the same time, the ball has a soft “feel” so that its flight path can be controlled on approach shots near the green.

Test Methods

Compression In the present invention, “compression” is measured according to a known procedure, using an Atti compression test device, wherein a piston is used to compress a ball against a spring. The travel of the piston is fixed and the deflection of the spring is measured. The measurement of the deflection of the spring does not begin with its contact with the ball; rather, there is an offset of approximately the first 1.25 mm (0.05 inches) of the spring's deflection. Cores having a very low stiffness will not cause the spring to deflect by more than 1.25 mm and therefore have a zero compression measurement. The Atti compression tester is designed to measure objects having a diameter of 1.680 inches; thus, smaller objects, such as golf ball cores, must be shimmed to a total height of 1.680 inches to obtain an accurate reading. Conversion from Atti compression to Riehle (cores), Riehle (balls), 100 kg deflection, 130-10 kg deflection or effective modulus can be carried out according to the formulas given in J Dalton.

Coefficient of Restitution (COR) In the present invention, COR is determined according to a known procedure, wherein a golf ball or golf ball subassembly (for example, a golf ball core) is fired from an air cannon at two given velocities and a velocity of 125 ft/s is used for the calculations. Ballistic light screens are located between the air cannon and steel plate at a fixed distance to measure ball velocity. As the ball travels toward the steel plate, it activates each light screen and the ball's time period at each light screen is measured. This provides an incoming transit time period which is inversely proportional to the ball's incoming velocity. The ball makes impact with the steel plate and rebounds so it passes again through the light screens. As the rebounding ball activates each light screen, the ball's time period at each screen is measured. This provides an outgoing transit time period which is inversely proportional to the ball's outgoing velocity. The COR is then calculates as the ratio of the ball's outgoing transit time period to the ball's incoming transit time period (COR=V_(out)/V_(in)=T_(in)/T_(out)).

Hardness The surface hardness of a golf ball layer (or other spherical surface) is obtained from the average of a number of measurements taken from opposing hemispheres, taking care to avoid making measurements on the parting line of the core or on surface defects such as holes or protrusions. Hardness measurements are made pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic by Means of a Durometer.” Because of the curved surface of the golf ball layer, care must be taken to ensure that the golf ball or golf ball subassembly is centered under the durometer indentor before a surface hardness reading is obtained. A calibrated digital durometer, capable of reading to 0.1 hardness units, is used for all hardness measurements and is set to take hardness readings at 1 second after the maximum reading is obtained. The digital durometer must be attached to and its foot made parallel to the base of an automatic stand. The weight on the durometer and attack rate conforms to ASTM D-2240. It should be understood that there is a fundamental difference between “material hardness” and “hardness as measured directly on a golf ball.” For purposes of the present invention, material hardness is measured according to ASTM D2240 and generally involves measuring the hardness of a flat “slab” or “button” formed of the material. Surface hardness as measured directly on a golf ball (or other spherical surface) typically results in a different hardness value. The difference in “surface hardness” and “material hardness” values is due to several factors including, but not limited to, ball construction (that is, core type, number of cores and/or cover layers, and the like); ball (or sphere) diameter; and the material composition of adjacent layers. It also should be understood that the two measurement techniques are not linearly related and, therefore, one hardness value cannot easily be correlated to the other.

The invention is further illustrated by the following examples, although these examples should not be construed as limiting the scope of the invention.

EXAMPLES

The following Tables I-IV contain prophetic examples of linear functionalized polyethylene copolymer compositions that may be used to make the golf balls of this invention. As discussed above, the compositions may be used to make any layer in the golf balls including, but not limited to, an outer core, intermediate layer, inner cover, and/or outer cover. In the following examples, the composition comprises a linear functionalized ethylene copolymer having 15 wt % acrylic acid comonomer neutralized with various counter-cations. Melt flow modifiers such as a metal salt of fatty acid may be added to the composition. The compositions provide the golf ball with improved resiliency and impact durability and other favorable properties.

TABLE I (Prophetic Examples) Linear Functionalized Polyethylene Having 15 Wt. % Acrylic Acid Neutralized With Sodium Hydroxide. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 parts) parts) (parts) (parts) (parts) (parts) Linear 100 100 100 100 100 100 Functionalized Polyethylene having 15.0 wt % of acrylic acid NaOH 0.832 1.664 2.496 3.328 3.744 4.160 Target 20 40 60 80 90 100 Neutralization

TABLE II (Prophetic Examples) Linear Functionalized Polyethylene Having 15 Wt. % Acrylic Acid Neutralized With Sodium Hydroxide In The Presence Of Zinc Stearate (Flow Modifier). Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 parts) parts) (parts) (parts) (parts) (parts) Linear 100 100 100 100 100 100 Functionalized Polyethylene having 15.0 wt. % of acrylic acid NaOH 0.832 1.664 2.496 3.328 3.744 4.160 Zinc stearate — — 10 20 30 45 Target 20 40 60 80 90 100 Neutralization

TABLE III (Prophetic Examples) Linear Functionalized Polyethylene Having 15 Wt. % Acrylic Acid Neutralized With Magnesium Hydroxide. Ex. 13 Ex. 14 Ex. 154 Ex. 16 Ex. 17 Ex. 18 parts) parts) (parts) (parts) (parts) (parts) Linear 100 100 100 100 100 100 Functionalized Polyethylene having 15.0 wt. % of acrylic acid Magnesium 1.217 2.426 3.639 4.852 5.459 6.055 hydroxide Target 20 40 60 80 90 100 Neutralization

TABLE IV (Prophetic Examples) Linear Functionalized Polyethylene Having 15 Wt. % Acrylic Acid Neutralized With Magnesium Hydroxide In The Presence Of Zinc Stearate (Flow Modifier). Ex. 19 Ex. 20 Ex. 21 Ex. 22 Ex. 23 Ex. 24 parts) parts) (parts) (parts) (parts) (parts) Linear 100 100 100 100 100 100 Functional Polyolefin having 15.0 wt. % of acrylic acid Magnesium 1.217 2.426 3.639 4.852 5.459 6.055 hydroxide Zinc stearate — — 10 20 30 45 Target 20 40 60 80 90 100 Neutralization

It is understood that the golf balls having at least one layer made from a functionalized ethylene copolymer composition described and illustrated herein represent only presently preferred embodiments of the invention. It is appreciated by those skilled in the art that various changes and additions can be made to such golf balls without departing from the spirit and scope of this invention. It is intended that all such embodiments be covered by the appended claims. 

1. A golf ball having a core and at least one surrounding layer formed from a composition comprising a functionalized ethylene copolymer, wherein the functionalized ethylene copolymer has a linear or substantially linear structure and is produced by copolymerizing an ethylene monomer with a comonomer having a functional group in the presence of a metal-based catalyst selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, and platinum.
 2. The golf ball of claim 1, wherein the core comprises a rubber material.
 3. The golf ball of claim 2, wherein the rubber material is polybutadiene.
 4. The golf ball of claim 1, wherein the functional group is selected from the group consisting of sulfonic acid, sulfonic acid derivatives, chlorosulfonic acid, vinyl ethers, vinyl esters, primary amines, secondary amines, tertiary amines, mono-carboxylic acids, dicarboxylic acids, partially or fully ester derivatized mono-carboxylic acids, partially or fully ester derivatized dicarboxylic acids, anhydrides of dicarboxylic acids, cyclic imides of dicarboxylic acids, and ionomeric derivatives thereof.
 5. The golf ball of claim 4, wherein the functional group is acrylic or methacrylic acid.
 6. The golf ball of claim 4, wherein the functional group is an acrylate or methacrylate.
 7. The golf ball of claim 4, wherein the functional group is selected from the group consisting of maleic anhydride, maleic acid, and maleate ester.
 8. The golf ball of claim 1, wherein the acrylic or methacrylic acid is neutralized to less than 70% by a cation source.
 9. The golf ball of claim 1, wherein the acrylic or methacrylic acid is neutralized to greater than 70% by a cation source.
 10. The golf ball of claim 1, wherein the maleic anhydride, maleic acid, or maleate ester is neutralized to less than 70% by a cation source.
 11. The golf ball of claim 1, wherein the maleic anhydride, maleic acid, or maleate ester is neutralized to greater than 70% by a cation source.
 12. The golf ball of claim 1, wherein the functionalized ethylene copolymer further comprises an α-olefin comonomer having 3 to 20 carbon atoms.
 13. The golf ball of claim 12, wherein the α-olefin comonomer is selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene.
 14. The golf ball of claim 1, wherein the composition comprising the functionalized ethylene copolymer has a flexural modulus in the range of about 10 to about 100 kpsi.
 15. The golf ball of claim 1, wherein the composition comprising the functionalized ethylene copolymer has a material hardness in the range of about 25 to about 75 Shore D.
 16. The golf ball of claim 1, wherein the composition comprising the functionalized ethylene copolymer has an elongation at break of about 100 to about 400%.
 17. The golf ball of claim 1, wherein the composition comprising the functionalized ethylene copolymer has a tensile strength at break of about 1 to about 7 kpsi.
 18. The golf ball of claim 1, wherein the metal-based catalyst is a ruthenium-based catalyst having the following structure:

wherein L₁ and L₂ are independently selected from the group consisting of alkyl phosphine, aryl phosphine, 1,3-dimesitylimidazol-2-ylidene, 1,3-di(2,6-diisopropylphenyl)imidazol-2-ylidene, 1,3-diarylimidazol-2-ylidene, 1,3-dimesitylimidazolidin-2-ylidene, 1,3-di(2,6-diisopropylphenyl)imidazolidin-2-ylidene, 1,3-diphenyltriazine, and pyridine; L₃, if present, is pyridine and is identical to L₂; and R₄ is selected from the group consisting of hydrogen, C₁-C₂₀ linear alkyl, C₁-C₂₀ branched alkyl, C₁-C₂₀ cycloalkyl, C₁-C₂₀ alkenyl, aryl and phenyl.
 19. The golf ball of claim 1, wherein the ball comprises an intermediate layer overlying the core and a cover layer overlying the intermediate layer, the intermediate layer being formed from the composition comprising the functionalized ethylene copolymer.
 20. The golf ball of claim 19, wherein the intermediate layer has a thickness in the range of about 0.010 to about 0.030 inches and a Shore D material hardness in the range of about 50 to about
 75. 21. The golf ball of claim 19, wherein the cover layer is made of a thermoplastic or thermoset polyurethane, polyurea, or polyurethane/polyurea hybrid composition.
 22. The golf ball of claim 19, wherein the cover layer is made of an ionomer resin.
 23. The golf ball of claim 1, wherein the ball further comprises an intermediate layer overlying the core and a cover layer overlying the intermediate layer, the cover layer comprising an inner cover layer and surrounding outer cover layer, the inner cover layer being formed from the composition comprising the functionalized ethylene copolymer.
 24. The golf ball of claim 23, wherein the inner cover layer has a thickness in the range of about 0.020 to about 0.500 inches and a Shore D material hardness in the range of about 50 to about
 70. 25. The golf ball of claim 23, wherein the outer cover layer is made of a thermoplastic or thermoset polyurethane, polyurea, or polyurethane/polyurea hybrid composition.
 26. The golf ball of claim 23, wherein the outer cover layer is made of an ionomer resin.
 27. The golf ball of claim 1, wherein the ball further comprises an intermediate layer overlying the core and a cover layer overlying the intermediate layer, the cover layer comprising an inner cover layer and surrounding outer cover layer, the intermediate layer being formed from the composition comprising the functionalized ethylene copolymer.
 28. The golf ball of claim 1, wherein the ball further comprises an intermediate layer overlying the core and a cover layer overlying the intermediate layer, the core having an inner portion and a surrounding outer core layer, the outer core layer being formed from the composition comprising the functionalized ethylene copolymer. 